It’s not even New Year’s Day yet, and there’s an apparent date bug causing problems for iPhone owners. Around the world, users are reporting that after 12:15 AM, incoming notifications from apps that use daily or repeat settings can cause their devices to suddenly use 100 percent of the CPU and then soft reset. According to iMore, the problem seems to be tied to locally generated notifications, as opposed to notifications internet services send to your phone.
If you’re affected by this issue, the best fix appears to be disabling notifications from any apps that use the local settings. You can try resetting your date to December 1st, but that may cause other problems. So far Apple has not publicly commented on the issue, but posters on the company’s support forums and Reddit say that phone reps have informed them iOS 11.2 includes a fix for this issue.
I can predicate that tomorrow, Apple Store will be hell… and probably some team will be on-call at Apple and need to be in office… 🤔
— Yoshimasa Niwa (@niw) December 2, 2017
PSA: iPhone Reboot/Respring Issues Megathread from iphone
Source: Apple Support forum, r/iPhone